The present invention relates to a refrigeration apparatus including a high-temperature-side refrigerant circuit and a low-temperature-side refrigerant circuit each constituting an independent refrigerant closed circuit in which a refrigerant discharged from a compressor is condensed and then evaporated to exert a cooling function, an evaporator of the high-temperature-side refrigerant circuit and a condenser of the low-temperature-side refrigerant circuit constituting a cascade heat exchanger, an evaporator of the low-temperature-side refrigerant circuit being configured to cool a storage chamber constituted in an insulating box body to an extremely low temperature.
Heretofore, a two-dimensional refrigeration apparatus has been used as a refrigeration apparatus having an extremely low temperature for use in storing, for example, cells, microorganisms and the like in a biological field. FIG. 10 shows a refrigerant circuit diagram of a refrigeration apparatus 135 using the two-dimensional refrigeration apparatus. A refrigerant circuit 100 is constituted of a high-temperature-side refrigerant cycle 101 and a low-temperature-side refrigerant cycle 102. A discharge-side pipe 103D of a compressor 103 constituting the high-temperature-side refrigerant cycle 101 is connected to an auxiliary condenser 105, and the auxiliary condenser 105 is connected to a frame pipe 104 (for the frame pipe, refer to a frame pipe 27 of the present application), and then connected to a condenser 107 via an oil cooler 106 of the compressor 103. The condenser 107 is cooled by a blower 116 for the condenser. Moreover, an outlet-side refrigerant pipe of the condenser 107 is connected to an evaporator 110 as an evaporator portion constituting the evaporator successively through a drier 108 and a pressure reducing unit 109. An outlet-side refrigerant pipe of the evaporator 110 is connected to an accumulator 111, and a refrigerant pipe exiting from the accumulator 111 is connected to a suction-side pipe 103S of the compressor 103.
On the other hand, a discharge-side pipe 113D of a compressor 113 constituting the low-temperature-side refrigerant cycle 102 is connected to an oil separator 114, and a refrigerant pipe connected to the outlet side of this oil separator 114 is connected to a condensing pipe 115 as a high-temperature-side pipe inserted into the evaporator 110. This condensing pipe 115 constitutes a cascade heat exchanger 130 together with the evaporator 110.
Moreover, a discharge pipe connected to the outlet side of the condensing pipe 115 is connected to a first gas-liquid separator 116 through a drier 131, and the gas-phase refrigerant separated by the gas-liquid separator 116 passes through a first intermediate heat exchanger 117 via a gas-phase pipe to flow into a second gas-liquid separator 118. A liquid-phase refrigerant separated by the gas-liquid separator 116 passes through a drier 119 and a pressure reducing unit 120 via a liquid-phase pipe, flows into the first intermediate heat exchanger 117, and evaporates the gas-phase refrigerant to cool.
The liquid-phase refrigerant separated by the second gas-liquid separator 118 passes through a drier 121 and a pressure reducing unit 122 via the liquid-phase pipe to flow into a second intermediate heat exchanger 123. The gas-phase refrigerant separated by the second gas-liquid separator 118 passes through the second intermediate heat exchanger 123 via the liquid-phase pipe, and passes through a third intermediate heat exchanger 124 and a drier 125 to flow into a pressure reducing unit 126. The pressure reducing unit 126 is connected to an evaporation pipe 127 as an evaporator arranged in a heat exchanging manner in an inner wall of an insulating box body 132 of the refrigeration apparatus on a storage chamber side, and the evaporation pipe 127 is further connected to the third intermediate heat exchanger 124.
The third intermediate heat exchanger 124 is successively connected to the second and first intermediate heat exchangers, and then connected to a suction-side pipe 113S of the compressor 113. This suction-side pipe 113S is connected to an expansion tank 128 for receiving the refrigerant during the stop of the compressor 113 through a pressure reducing unit 129.
In this refrigeration apparatus 135, the evaporation pipe 127 of the low-temperature-side refrigerant cycle 102 reaches an extremely low temperature of −150° C. or less, and even the cascade heat exchanger 130 reaches a low temperature of about −40° C. Therefore, a cascade heat exchanger 130 part needs to be sufficiently insulated. In a conventional constitution, as shown in FIG. 11, the cascade heat exchanger 130 is provided with an externally opened storage recess portion 133 beforehand secured in the back surface of the insulating box body 132 constituting the main body of the refrigeration apparatus 135, and the heat exchanger is incorporated after foaming an insulating material of the insulating box body 132 (see Japanese Patent Application Laid-Open No. 2000-105047).
Moreover, in the peripheral surface of this cascade heat exchanger 130, the insulating material is positioned, and a flat-plate-like insulating material 134 is received in a space between the storage recess portion 133 and the cascade heat exchanger 130 so as to cover the whole opening.
However, since the cascade heat exchanger 130 has a low temperature of about −40° C., dew might be attached to the outer surface of the main body around the heat exchanger. Therefore, the corresponding part needs to be sufficiently insulated, and an insulating structure is constituted so that the thickness of the insulating material 134 is remarkably increased, and the material is covered with a cover part from the outside. However, when the thickness of the insulating material 134 is increased, a protruding part corresponding to the thickness of the insulating material 134 is present in the back surface part of the main body, which causes a problem that the protruding part disturbs the installation of the refrigeration apparatus 135.
In particular, in a case where the refrigeration apparatus 135 is carried indoors, there sometimes occurs a disadvantage that the apparatus is stuck in the carrying entrance of an installation place and that it becomes difficult to carry the apparatus indoors. Therefore, to smoothly perform a carrying operation, in a case where a product is designed so that the thickness of the insulating material of this protruding part is secured over the whole main body, there is a problem that when an outer dimension is not increased, a volume in the storage chamber decreases.
To solve the problem, in a refrigerator disclosed in Japanese Patent Application Laid-Open No. 2000-105047, a constitution is employed in which the insulating material covering the back surface of the cascade heat exchanger is covered with an inner cover, a second insulating material and an outer cover covering the material are provided outside the inner cover, and the outer cover is detachably attached to the inner cover with a plurality of small screws. In consequence, during the carrying, the carrying operation of the refrigeration apparatus is performed in a state in which the outer cover is removed, which avoids a disadvantage that the protruding part is stuck in the carrying entrance as described above.
However, according to such a constitution, even in the installation place, the protruding part is still present in the back surface part of the main body. Even in such a case, owing to the product design in which the thickness of the protruding part is secured over the whole main body, there has been a problem that the storage volume decreases with respect to a depth as the outer dimension. Moreover, there has been a problem that an operation of attaching the outer cover needs to be performed after the installation, thereby resulting in a laborious carrying operation.